If they're not lighting LED's (use a lot of power), it should work fine. When I first started breadboarding electronics, I used a 5V wall wart for my power supply. You can also use an old desktop computer power supply which has 3.3, 5, and 12V taps. You can get a basic DC power supply pretty cheap though, like this.

Yes, you could play with that...maybe save it for something you build that it would "fit" well....as Craig said, try to find an old computer power supply with several taps.

You can then set it up as a workbench supply (until you get the urge to BUILD one!), and likely can work it up to give 12V, 9V, and the necessary 5V, with regulation. Many also offer split supplies, so you can have +12v and -12V, as well! Look into a supply with a regulator, like a LM317 and a good 24V transformer if you want something *really good* for the workbench.

This is great for testing and designing.....then, if you find something that needs , oh, maybe 5v at 100mA, you might be able to use the phone supply (I'd guess the lower the current draw, the higher the voltage - test this, it's a good 'understanding' exercise! It should give 4.2v AT +/- 350mA, and higher if you draw less...). Remember to determine wattage (Voltage X Current in A) before you start hooking up resistors

I save all the walwarts that come my way, and tailor them for projects that I'll make permanent. Often requires placing a regulator on the board, maybe just a zener or a dedicated one.....sometimes they're just "plug and play"! They're worth keeping and experimenting with.